The second will be redefined — optical clocks on the way to 2030
Optical clocks are already about a hundred times more accurate than the caesium fountains behind today’s definition of the second. The conference on weights and measures is to approve a roadmap towards a new definition with a 2030 date.
- The second is defined today by a transition in the caesium atom — as written down in 1967.
- Optical clocks, based on transitions at much higher frequencies, are already about a hundred times more accurate than the best caesium fountains.
- Accuracy is one thing, agreement another: different optical clocks in different countries must give the same result and be comparable.
- So a roadmap towards the change was adopted rather than the change itself: repeatable international comparisons, continuous clock operation and demonstrated uncertainty — a redefinition in 2026 would be premature, the target is 2030.
- The second will not run differently because of it — what changes is the top of the reference chain, and with it the wording of time and frequency calibration certificates.
- It is worth following the announcements of the national metrology institute, because a rebuild at the top will in time reach ordinary calibrations.
Source: BIPM